The Canadian Environmental Protection Act (CEPA) requires that the Ministers of Environment and Health prepare a list of substances that should be given priority for assessment to determine whether they are "toxic" as defined under Section 64 of the Act. This list is known as the Priority Substances List (PSL).

To help Canadians understand how the risks posed by toxic substances are assessed, Environment Canada has released a guidance manual, Environmental Assessments of Priority Substances Under the Canadian Environmental Protection Act, which outlines the scientific environmental assessment process under the Priority Substances Assessment Program (PSAP). Substances are also assessed by Health Canada to determine their effects on human health. Information on human health risk assessments is available from Health Canada’s Bureau of Chemical Hazards.

The manual is intended primarily for use by people leading environmental risk assessments of priority substances, and the groups of experts who assist them. It will also be of interest to other organizations and individuals wishing to understand how Environment Canada conducts such assessments.

The first step in an environmental assessment is to develop a Problem Formulation, in which the goals and focus of the assessment are stated and the strategy for proceeding with the assessment is outlined. In the analysis, or second phase of the assessment, information on a substance’s entry into the environment, the concentration to which animals and plants are exposed, and its effects on organisms or ecosystems are analyzed. The third phase, known as risk characterization, compares exposure concentrations and concentrations causing effects to determine if adverse effects are likely.

In determining whether a substance should be declared "toxic" under CEPA, the likelihood and magnitude of releases into the environment and the harm it may cause to human health or ecosystems at levels occurring in the Canadian environment are taken into account. If a substance is found to be "toxic," the federal government works with the provinces, territories, industry, nongovernment organizations and other interested parties to develop a management plan to reduce or eliminate the harmful effects the substance has on the environment and the health of Canadians.

A condensed version of the Guidance Manual is available, or the entire text of the Guidance Manual can be downloaded. Printed copies can also be ordered from:

Environmental Protection Service Publications
Environmental Technology Advancement Directorate
Environment Canada
Tel.: (819) 953-5750
Fax: (819) 953-7253
e-mail: epspubs@ec.gc.ca